USDA Forest Service

Forest Health Protection, Southern Region


USDA Forest Service
Forest Health Protection
Region 8
1720 Peachtree Road, NW
Room 816 N
Atlanta, GA 30309

Phone: (404) 347-7478
Fax: (404) 347-1880

United States Department of Agriculture Forest Service.

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caused by Melampsora medusae


Importance. - All sizes of cottonwood are affected, but cottonwood rust is particularly severe in plantations and nurseries. Heavy infection and subsequent defoliation may kill trees. The rust may also act as a predisposing agent to other diseases. Affected trees may be partially or completely defoliated.

Identifying the Fungus. - Yellow or orange pustules, containing spores, form on the under-surface of the leaves in midsummer. These are replaced by dark brown fungal growths in the fall.

Biology. - The orange pustules (uredia) are the summer reproductive state of the fungus. They are followed by dark brown pustules (telia) which develop in fall and winter. In the South, the alternate host (larch) is not present in the forest, and the fungal life cycle is reduced to the urediaurediospore cycle only. Some families are immune to rust infection and disease-free trees or groups of trees often occur in the midst of other heavily infected trees.

Control. - Resistant varieties of cottonwood are used to minimize damage. Generally, no control is attempted in forest stands.



Rust infected cottonwood leaf

Rust infected cottonwood leaf.



USDA Forest Service - Forest Health Protection, Southern Region
Last Modified: Monday, 16 December 2013 at 14:18:29 CST

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